Protests, some deadly, erupted across the Muslim world today as anger spread over an amateur anti-Islam film produced in the U.S. American symbols - including embassies, schools and restaurants - were attacked. In Egypt, protesters took to the streets for the fourth straight day. Egyptian soldiers built a wall to protect the U.S. Embassy, and Islamist President Mohammed Morsi denounced the attacks.

Yesterday, Morsi received a call from President Obama. The message, say U.S. officials: don't fuel the flames. Observers say Morsi and the powerful Muslim Brotherhood are walking a fine line. As NPR's Leila Fadel reports, they're trying to address U.S. concerns while placating an angry public.

UNIDENTIFIED MAN: (Foreign language spoken)

LELIA FADEL, BYLINE: Just outside the U.S. Embassy, young men try to get around the wall blocking their path to the diplomatic mission. Riot police bombard them with teargas, taking no chances that an angry mob will breach the walls of the fortified compound again.

An amateur anti-Muslim film posted on YouTube and produced in the United States by a Coptic Christian has sparked angry and, in some cases, fatal protests across the Muslim world. In Libya, a U.S. ambassador and three staffers were killed, and today, smoke billowed from the embassy in Tunisia.

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FADEL: The protests in Cairo show no signs of letting up. Egypt's new Islamist president is facing the biggest diplomatic crisis of his presidency. On the one hand, he wants to show his piety and outrage over the film that mocks the Muslim prophet. But he must also safeguard American diplomats and preserve the vital relationship with Washington.

Observers say this is the first true test to the U.S. relationship with the new Islamist authority in Egypt. That came into sharp focus earlier this week when President Obama was asked in a Telemundo interview aired on MSNBC if Egypt is an ally of the United States.

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PRESIDENT BARACK OBAMA: I don't think that we would consider them an ally, but we don't consider them an enemy. They are a new government that is trying to find its way.

FADEL: The administration leader backed away from the statement. Obama also made a firm phone call to President Morsi yesterday, demanding that he protect American diplomats. Jay Carney, the White House spokesman, described the call at a briefing today.

JAY CARNEY: As you know, the president had an important conversation with President Morsi about the need to protect our embassy and our personnel in Cairo and the need to denounce the violence.

FADEL: Observers say the threat of estrangement with Washington worked. Morsi condemned the attack personally from Brussels on Thursday for the first time in an address to the nation aired on state TV.

PRESIDENT MOHAMMED MORSI: (Foreign language spoken)

UNIDENTIFIED GROUP: (Foreign language spoken)

FADEL: Today, the Brotherhood canceled a call for nationwide protests, but in northern Egypt, Brotherhood led demonstrations happened anyway with people calling for the boycott of American products and in some cases an end to relations with the U.S. Elsewhere in Sinai, protesters attacked the compound of international peacekeepers, setting fire to a watchtower and a fire truck, according to security officials. Gehad Haddad, a spokesman for the Brotherhood, said the organization finds itself in uncharted waters.

GEHAD EL-HADDAD: They're walking an incredibly fine line that they have never been trained to walk before.

FADEL: In the past, the organization was persecuted and only answered to its base. The United States supported the autocratic government that oppressed it and other opposition groups. Now, the Muslim Brotherhood is the authority in the new Egypt, and its every move is under an international spotlight.

The Brotherhood sent a delegation to the protest yesterday to reason with the angry demonstrators and another this morning. But they were ridiculed and forced away. Even the president's adviser's phone was stolen. Haddad said that Morsi's opponents are using this opportunity to paint him as soft on America and less Islamic than other more fundamentalist factions.

There are deep-seated grievances in the Arab world against the United States for a foreign policy that long favored dictators that oppressed their people. But he doesn't think it will damage the relationship with Washington.

EL-HADDAD: There's two ways this can progress: either we start denouncing each other - and that will only serve the very nature of why this movie was created - and make sure that Egypt is more isolated and the U.S. is more hated in the world.

FADEL: Or, he says, Egypt and the United States can have a mutually beneficial relationship. Egypt is a democracy now, he adds. Gone are the days when a ruler told his people how to think, and the United States has to understand that. Leila Fadel, NPR News, Cairo. Transcript provided by NPR, Copyright NPR.